The research proposed is directed toward the study, on a molecular level, of a set of coordinately controlled genes in a eukaryote. These are the ribosomal protein genes of Drosophila melanogaster. This work will include: (a) the study of the kinetics of synthesis of the ribosomal proteins with respect to each other and to the ribosomal RNAs; and (b) the study of the location of some of the mRNAs coding for these proteins, both on the chromosomal level and on long DNA strands. In order to detect the ribosomal proteins present in very small amounts in total cellular homogenates, and to selectively isolate their mRNAs new technology is required. The procedure proposed has two novel features: (a) it will allow the detection and isolation of small amounts of protein from cell cytoplasm and cell organelles; and the same methods can be adapted to the selective isolation of the mRNAs coding for these proteins. This new methodology will potentially be of use in the study of many other systems as well as this one. The results of this study will be used to evaluate the timing of expression of the various ribosomal protein genes and their chromosomal location with a view toward understanding the molecular basis for regulation of this set of essential protein genes in a eukaryote.